1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile apparatus employing an electrophotographic system as an image forming method, and more particularly to an image forming apparatus furnished with a transfer device for transferring a developer image formed on an image carrier onto a transfer material.
2. Description of the Related Art
In an image forming apparatus employing an electrophotographic photoconductor (hereafter abbreviated as xe2x80x9cphotoconductorxe2x80x9d) as an image carrier, image formation is achieved as follows. Firstly, the surface of the photoconductor is uniformly charged by a charging device and is thereafter exposed to light by an optical recording device so as to form an electrostatic latent image. Subsequently, the resultant electrostatic latent image is developed in a development device using a developer, and a developer image carried on the photoconductor is transferred onto a conveyed recording material by a transfer device. Lastly, the transferred developer image is fixed onto the recording material by a fixing device. The recording material onto which the developer image is fixed is available to users, for example, as an item representing an image.
Recently, in an image transfer process for transferring a developer image onto a recording material, there has been widely used a transfer system for performing transfer by bringing a transfer body, such as a transfer roller, transfer brush, or transfer block, into proximity to or abutment with a surface of an image carrier. This is because, this transfer system generates less ozone than a conventional electrostatic transfer system which exploits a discharge triggered by a corona discharge wire, and is therefore one of environmentally-friendly transfer systems.
However, in the above-stated transfer system for performing transfer by bringing a transfer body, such as a transfer roller, transfer brush, or transfer block, into proximity to or abutment with a surface of an image carrier, allowance of space for conveyance of a transfer material is less than in the conventional electrostatic transfer system employing a corona discharge wire. Thus, high conveyance accuracy is required.
That is, if the conveyance accuracy is low, the following problems arise. The transfer material tends to be deviated from a conveying path and may possibly be brought into contact with members arranged nearby, resulting in a bending or paper jam. Moreover, if the transfer material makes contact with the nearby members, a developer image having been already transferred is disturbed, or residual toner remaining on the surface of the image carrier, as well as toner scattered around the image carrier, inconveniently adhere to the surface of the transfer body, which has an adverse effect on the transfer process. Further, for example, environmental factors such as humidity surrounding the apparatus and the firmness of the transfer material are expected to vary widely. This makes it difficult to convey the transfer material in a wider range.
Specifically, there exist the following problems. During image formation is being conducted on a plurality of transfer materials, between the instant when image formation on a preceding transfer material is completed and the instant when a front-end portion of a subsequent transfer material enters opposed portions of the image carrier and the transfer body, namely, in a state where the transfer material is not present between the image carrier and the transfer body, the transfer body is inconveniently brought into direct contact with the surface of the image carrier. Consequently, toner stuck to the image carrier adheres to the surface of the transfer body. As a rear-end portion of the subsequent transfer material comes out of the opposed portions of the image carrier and the transfer body, the rear-end portion of the transfer material rubs against the surface of the transfer body with toner, and the toner undesirably stuck to the transfer body adheres to the rear-end portion of the transfer material, which results in the rear-end portion being stained. As a result, if the transfer material kept in a stained state is subjected to fixing process, the toner stuck to the rear-end portion is inconveniently fixed to the transfer material, and thus it is inevitable that the rear-end portion of the transfer material is stained.
An object of the invention is to provide an image forming apparatus which is capable of, despite having a simple structure, conveying a transfer material properly and securely even in a case where allowance of space is limited, for example, where an image carrier and a transfer body are arranged in proximate or abutting relation.
Another object of the invention is to provide an image forming apparatus which is capable of conveying a transfer material at a spaced interval with a transfer body so that a rear-end portion of the transfer material is kept out of abutment or contact with a surface of the transfer body.
The invention provides an image forming apparatus comprising:
an image carrier for carrying a developer image;
transfer means having a transfer body for electrostatically transferring the developer image carried on the image carrier onto a transfer material; and
transfer material guiding means disposed at a downstream side of opposed portions of the image carrier and the transfer body along a direction in which the transfer material is conveyed, for guiding the transfer material in conveyance by acting upon a reverse surface of the transfer material in such a manner that, when a rear-end portion of the transfer material passes through the opposed portions, the rear-end portion is kept away from the transfer body.
According to the invention, the transfer material guiding means, which is disposed at a downstream side of the opposed portions of the image carrier and the transfer body along a transfer material conveying direction, guides the transfer material in conveyance by acting upon the reverse surface of the transfer material in such a manner that, when the rear-end portion of the transfer material passes through the opposed portions, the rear-end portion is kept away from the transfer body. Thus, even in a case where sufficient space allowance cannot be ensured in the vicinity of the opposed portions of the image carrier and the transfer body, conveyance of a transfer material can be achieved properly and securely in a relatively simple structure. Particularly, since the rear-end portion of the transfer material having undergone a transfer process is unlikely brought into contact with the surface of the transfer body, the rear-end portion of the transfer material is free from toner stains.
In the invention, it is preferable that the transfer material guiding means includes a rotary body which is supported so as to be rotatable about an axis arranged parallel to a width direction of the transfer material that is perpendicular to the transfer material conveying direction.
According to the invention, as the transfer material is conveyed (transported) downstream along the transfer material conveying direction, the rotary body abutting on the reverse surface of the transfer material is rotated. This helps reduce friction with respect to the transfer material and thus allows the transfer material to be guidedly supported on a fixing side smoothly.
In the invention, it is preferable that the transfer material guiding means includes a disc-shaped first guiding member and a second guiding member having a star-shaped axially perpendicular section, the first and second guiding members being integrally supported so as to be rotatable about the axis arranged parallel to a width direction of the transfer material that is perpendicular to the transfer material conveying direction.
According to the invention, the transfer material guiding means includes the disc-shaped first guiding member and the second guiding member having a star-shaped axially perpendicular section, and the first and second guiding members are integrally supported so as to be rotatable about the axis arranged parallel to the width direction of the transfer material that is perpendicular to the transfer material conveying direction. Thus, damage to a front-end portion of the transfer material can be reduced to minimum that is caused when the front end of the transfer material comes into collision with the transfer material guiding means. Moreover, when the transfer material guiding means guides the transfer material toward the fixing side by acting upon the reverse surface of the transfer material, an area of the contact surface between the reverse surface of the transfer material and the transfer material guiding means can be kept minimum. This allows the transfer material to be guidedly supported smoothly.
Further, in this construction, the extremity of the second guiding member is adequately engaged with the front-end portion of the transfer material. Therefore, the first and second guiding members, constituting the transfer material guiding means, can be integrally rotated with ease, thereby suppressing friction between the transfer material guiding means and the transfer material. In addition, the outer circumferential edge portion of the first guiding member serves to prevent the transfer material or the like from entering between the extremities of the second guiding member.
In the invention, it is preferable that between the transfer body and the transfer material guiding means is disposed charge removing means for subjecting the transfer material to charge removal treatment.
According to the invention, the transfer material, onto which a developer image is transferred by the transfer body, is guided by the transfer material guiding means while being subjected to charge removal treatment by the charge removing means. Since the transfer material is guided by the transfer material guiding means, a distance between the transfer material being guided by the transfer material guiding means and the charge removing means can be kept constant at all times. This makes it possible to remove charges remaining on the entire surface of the transfer material uniformly.
In the invention, it is preferable that a plurality of the transfer material guiding means are arranged in accordance with a width of the transfer material, in a direction perpendicular to the transfer material conveying direction, in such a way as to be parallel to the width direction of the transfer material.
According to the invention, the plurality of the transfer material guiding means are arranged, in accordance with the width of the transfer material, in such a way as to be parallel to the width direction of the transfer material. This allows the entire transfer material being conveyed along the conveying path to be guidedly supported securely in its width direction.
In the invention, it is preferable that a plurality of the transfer material guiding means are respectively arranged so as to correspond to the periphery of both widthwise end portions of the transfer material and the periphery of the widthwise central portion thereof, so that the transfer material is guidedly supported at its reverse surface in such a way that the transfer material varies in its thickness-direction position from part to part.
According to the invention, a plurality of the transfer material guiding means respectively support, in the peripheries of the widthwise end portions and widthwise central portion of the transfer material, the transfer material at its reverse surface, and simultaneously guide it in such a way that the transfer material varies in its thickness-direction position from part to part. Consequently, in consideration of the distortion or warpage of the transfer material passing through the region between the image carrier and the transfer body, an adequate firmness can be secured in the transfer material, so that the sheet as a whole can be guidedly supported easily.
In the invention, it is preferable that the transfer material guiding means is made of an electrically conductive material.
In the invention, it is preferable that the transfer material guiding means includes a guiding member coated with an electrically conductive material.
According to the invention, the transfer material guiding means is made of an electrically conductive material, or includes a guiding member coated with an electrically conductive material. Therefore, it never occurs that the transfer material guiding means is inadvertently electrified due to friction between it and the reverse surface of the transfer material, and thus the transfer material can be guidedly supported with stability. Moreover, the developer image being electrostatically supported on the transfer material is protected from adverse effects caused by charges.
The invention further provides an image forming apparatus comprising:
an image carrier for carrying a developer image;
transfer means having a transfer body for electrostatically transferring the developer image carried on the image carrier onto a transfer material; and
transfer material guiding means disposed at a downstream side of opposed portions of the image carrier and the transfer body along a direction in which the transfer material is conveyed, the transfer material guiding means being rotated with conveyance of the transfer material by abutting on a surface of the transfer material opposite from a surface onto which the developer image is transferred.
According to the invention, the transfer material guiding means is disposed at a downstream side of the opposed portions of the image carrier and the transfer body along a transfer material conveying direction, and is rotated with conveyance of the transfer material by abutting on the surface of the transfer material opposite from the surface onto which the developer image is transferred. Thus, it is possible to reduce friction between the transfer material having passed through the opposed portions and the transfer material guiding means, thereby guidedly supporting the transfer material smoothly.
In the invention, it is preferable that the charge removing means includes a protective member which is made detachable, and that the transfer material guiding means is disposed on the protective member.
According to the invention, the transfer material guiding means is disposed on the detachable protective member. Accordingly, the transfer material guiding means can be detached from the charge removing means concurrently with detachment of the protective member from the charge removing means. This eliminates the need to detach the protective member and the transfer material guiding means separately for cleaning or replacement.